Ponderous Ark
Noetia ponderosa Say, 1822

Cut-ribbed Feature of the Ponderous Ark:
It's Groovy!

When I first posted this article, I mistakenly identified the shells in this photograph as the Cut-ribbed Ark (Anadara floridana Conrad, 1869). The bold longitudinal grooves in the ribs of these shells convinced me of their identification. Actually, these are further examples of the Ponderous Ark (Noetia ponderosa Say, 1822).

Jo O'Keefe (see OKeefes.org) used the article for reference while identifying Ark specimens, and sent a question to Dr. Harry G. Lee (see Jaxshells.org). Dr. Lee advised of the error in the article, noted that the Ponderous Ark also exhibits the cut-ribbed feature, and mentioned the following distinctions between the Ponderous Ark and the Cut-ribbed Ark:

• The Cut-ribbed Ark is almost never discovered on a beach, whereas the Ponderous Ark is a common beach find.
• The beak of the Ponderous Ark shell is narrowed and twisted so as to be pointed toward the noticeably angulate posterior (long end) of the shell, whereas the beak of the Cut-ribbed Ark is swollen and the posterior of the shell is more evenly rounded.
• The Ponderous Ark is usually around two inches across, whereas the Cut-ribbed Ark's size is more in the range of four inches. (Obviously there is significant variation: the dark Ponderous Ark shell in this illustration is three inches across.)

The Jaxshells.org website (for which Dr. Lee is scientific advisor) includes illustrations of both the Cut-ribbed Ark and the Ponderous Ark. Both species are also discussed and illustrated in Dr. Lee's book Marine Shells of Northeast Florida, Jacksonville Shell Club, Jacksonville, Florida, pp. 18, 20; species numbers 26, 36; color plates 1, 4.

Notes